blocxx
COWIntrusiveCountableBase.hpp
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33 
38 //
39 // Copyright (c) 2001, 2002 Peter Dimov
40 //
41 // Permission to copy, use, modify, sell and distribute this software
42 // is granted provided this copyright notice appears in all copies.
43 // This software is provided "as is" without express or implied
44 // warranty, and with no claim as to its suitability for any purpose.
45 //
46 
47 #ifndef BLOCXX_COW_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_
48 #define BLOCXX_COW_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_
49 
50 #include "blocxx/BLOCXX_config.h"
51 #include "blocxx/RefCount.hpp"
52 
53 namespace BLOCXX_NAMESPACE
54 {
55 
72 class COWIntrusiveCountableBase;
73 void COWIntrusiveReferenceAddRef(COWIntrusiveCountableBase * p);
74 void COWIntrusiveReferenceRelease(COWIntrusiveCountableBase * p);
75 bool COWIntrusiveReferenceUnique(COWIntrusiveCountableBase* p);
76 template <typename T> T* COWIntrusiveReferenceClone(T* p);
77 
78 class BLOCXX_COMMON_API COWIntrusiveCountableBase
79 {
80 private:
82 
83 protected:
88  : m_usecount(0)
89  {}
90 
97  {
98  // don't assign or change the ref count, since it won't be different.
99  return *this;
100  }
101 
105  COWIntrusiveCountableBase(): m_usecount(0)
106  {
107  }
108 
112  virtual ~COWIntrusiveCountableBase();
113 
117  RefCount getRefCount() const
118  {
119  return m_usecount;
120  }
121 
122 public:
129  {
130  p->m_usecount.inc();
131  }
132 
141  {
142  if (p->m_usecount.decAndTest())
143  delete p;
144  }
145 
153  {
154  return p->m_usecount.get() == 1;
155  }
156 
162  template <typename T>
163  friend T* COWIntrusiveReferenceClone(T* p);
164 };
165 
166 template <typename T>
168 {
169  // this needs to happen first to avoid a race condition between
170  // another thread deleting the object and this one making a copy.
171  T* tmp = p->clone();
172  if (p->m_usecount.decAndTest())
173  {
174  // only copy--don't need to clone, also not a race condition.
175  // undo the decAndTest.
176  p->m_usecount.inc();
177  delete tmp; // we won't need this anymore.
178  return p;
179  }
180  else
181  {
182  // need to become unique
183  if (tmp)
185 
186  return tmp;
187  }
188 }
189 
190 } // end namespace BLOCXX_NAMESPACE
191 
192 #endif
193 
194